Circuit Description
The engine coolant temperature (ECT) sensor is a variable resistor, that measures the temperature of the engine coolant. The ECT sensor has a signal circuit and a low reference circuit. The powertrain control module (PCM) supplies 5 volts to the ECT signal circuit and a ground for the ECT low reference circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively high ECT signal voltage, which is a low temperature indication, DTC P0118 sets.
Conditions for Running the DTC
The engine is running for more than 15 seconds.
Conditions for Setting the DTC
The ECT sensor temperature is less than -38°C (-36°F) for more than 24 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
If a short to a separate voltage source occurs this DTC may set and damage the ECT sensor. If this is found to be the condition, a continuity test to all other PCM circuits will be necessary to diagnose the specific fault.
After starting the engine, the ECT should rise steadily to about 90°C (194°F) then stabilize after the thermostat opens.
Use the Temperature vs Resistance Table in order to test the ECT sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. A skewed sensor could result in poor driveability concerns. Refer to Temperature Versus Resistance .
If a malfunction is not present at this time, refer to DTC P1115 .
If an intermittent condition is suspected refer to Intermittent Conditions .
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||
2 |
Does the scan tool indicate that the ECT sensor temperature is less than the specified value? | -38°C (-36°F) | Go to Step 4 | Go to Step 3 | ||||||||
3 |
Does the DTC reset? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||||||
Does the jumper fuse open? | -- | Go to Step 7 | Go to Step 5 | |||||||||
5 | Observe the ECT sensor temperature with a scan tool. Does the scan tool indicate that the ECT sensor temperature is more than the specified value? | 138°C (280°F) | Go to Step 9 | Go to Step 6 | ||||||||
6 |
Does the scan tool indicate ECT sensor temperature greater than the specified value? | 138°C (280°F) | Go to Step 8 | Go to Step 7 | ||||||||
7 |
Important: The sensor may be damaged if the circuit is shorted to a voltage source.
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 8 | ||||||||
8 |
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 | ||||||||
9 |
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11 | ||||||||
10 |
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12 | ||||||||
11 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||||
12 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||||
13 |
Does the DTC run and pass? | -- | Go to Step 14 | Go to Step 2 | ||||||||
14 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||
